Carbon dioxide reduction and carbon monoxide activation employing a reactive uranium(III) complex

The highly reactive, six-coordinate tris-aryloxide U(III) species, [((t-BuArO)3tacn)U] (1) reacts with CO2 in a 2e- reduction to produce CO and a dinuclear U(IV/IV) mu-oxygen bridged complex [{((t-BuArO)3tacn)U}2(mu-O)] (2). This reaction proceeds via a dinuclear CO2-bridged intermediate 3. Also, mononuclear 1 was treated with 1 atm of CO to yield dinuclear [{((t-BuArO)3tacn)U}2(mu-CO)] (4) with a CO ligand bridging two uranium ions in an unprecedented mu:eta1,eta1 fashion. The mixed-valent azido-bridged U(III/IV) complex 5 was synthesized from trivalent 1 and tetravalent [((t-BuArO)3tacn)U(N3)] and serves as an isostructural analogue of triatomic-bridged intermediate 3 as well as an electronic model for mixed-valent 4.